Recently, thanks to the micronization of research-grade devices, there’s been an increase in the use of muscle oxygenation in sports monitoring. Over the last few years, consumer products have entered the market, promising performance enhancement by using the data in training and recovery. A few systems have been validated to be useful in sports performance, making a guide on muscle oxygenation necessary for sport scientists, coaches, and medical professionals.
Included in this guide are expectations of the information, scientific validity, key features, and details of the hardware and software. As the wearable market continues to evolve and technology grows more refined, we expect that more sensors and better calculations will make muscle oxygenation even more popular. Down the road, the information from the sensors is likely to be a standard part of monitoring and testing athletes, and education on best practices is necessary.
What Is Near-Infrared Spectrometry?
Near-infrared spectrometry (NIRS) is a method of biological measurement that is non-invasive and engineered for real-time monitoring of basic physiological changes. NIRS uses light to penetrate the skin and sometimes into the muscle belly to detect rates of activity, specifically the hemoglobin and myoglobin in the vascular area. The typical locations for testing are the finger, temple of the head, and muscle belly of propulsive muscle groups. One sensor can measure general physiological health, while multiple sensors are needed for local muscle oxygenation. Single sensors have been used for estimating lactate responses in training, but they are not direct measures of lactate and require correction formulas to be in parallel with conventional blood readings.NIRS can detect, with a high degree of accuracy, changes in a few physiological systems in the body. Click To Tweet
NIRS can detect, with a high degree of accuracy, changes with a few physiological systems in the body, especially oxygen transfer under the skin. The use of NIRS ranges from low-level medical monitoring to sophisticated modeling of bioenergetics, all having unique validity and specific devices that can measure change in a human body. NIRS is not a new method of measurement, as it’s decades old and extremely useful for a wide range of needs.
The popularity of NIRS began in the 1980s and its use became typical years later in the medical, agricultural, and industrial fields. NIRS gained momentum in the performance world in the early 2000s. Today, nearly 20 years later, wearable and portable options are standard in the consumer space, and there are indications that NIRS has arrived in elite and recreational sport.
Different wavelengths of light have specific value in the medical industry, and for the use of sports monitoring today, most of the wavelengths are in the higher ranges. Similar technologies that are available and should not be confused with NIRS include photoplethysmography (PPG), laser Doppler flowmetry (LDF), and pulse oximetry (PO). These measures do use non-invasive technology similar to NIRS, but are separate biological measures.
Local oxygenation of a muscle is easier to interpret, but still requires a lot of understanding of core physiology. Body temperature, motion artifacts, and simple anatomical understanding all play a role in interpreting the data collected from NIRS devices. Additional physiological systems are often combined when monitoring athletes, such as heart rate monitors, gas exchange devices, and even electrocardiograms.
How Are Muscle Oxygenation and Other Measurements Calculated?
Muscle oxygenation is calculated by an algorithm, thus making an indirect measurement. Most non-invasive measures are estimations, and any NIRS product must be validated against gold standards and compared to systems that have been validated to see if the data is close or interchangeable. It’s possible to have a system that is not as accurate as a research-grade system but still very reliable, making it useful to detect change, but the absolute numbers are not indicative of what is truly happening in the body. Since the calculations of algorithms with NIRS devices are static and don’t factor in sweat rates and other environmental factors, including motion artifacts, careful interpretation is needed to conjecture on what is happening internally within the muscle group tested. More sensors are usually added to compare with other muscle groups for additional perspective, including non-working muscles for contrast analysis.
Measurement begins with light-emitting diodes (LED) firing and projecting waves through the skin and fat and into the muscle. The lights are painless, are not surgical lasers or similar, and are, in fact, completely safe. The sensors inside the NIRS system pick up the scattered light reflected within the biological tissue, and estimate what is happening based on the status of oxygenated and deoxygenated cells in the bloodstream. This process, while simple, requires a lot of research and experimentation to properly analyze a very complex physiological response in exercise so that the calculations are valid, accurate, and precise enough for sport use.
What Is a NIRS System Useful for in Sport?
Near-infrared spectrometry is valuable because it’s continuous, specific, and non-invasive. Muscle monitoring is the most common use, but functional locations (head) are growing and practitioners use fNIRS (functional NIRS) to designate the specifics of the head location over local areas of the body. NIRS is useful for monitoring the change in oxygenation of muscles, therefore it can serve as an excellent proxy to the lactate response and even estimate the contribution from mitochondrial adaptations.
Based on the research, each measurement of the body is unique and ranges from very accurate and reliable to more limited. Nearly all of the benefits to athletes are with conditioning, but some strength training monitoring is possible with NIRS systems. The market caters mainly to endurance training, but speed and power sports, specifically hockey, are adopting the technology as well.
Total body lactate readings are not interchangeable with NIRS measurements for the most part, mainly because the sensors look at the specific muscle, and the specific muscle group may not represent an entire body. General relationships of training and local muscle oxygenation do have merit when coaches want to see higher rates of work, as a few calculations do provide adequate representations of the lactate response, but the values are not absolute and are more working standards for internal tracking. Multiple sensors and correction formulas are necessary to help model lactate responses. If absolute measurements are necessary, conventional lactate testing should be considered.If absolute measurements are necessary, conventional lactate testing should be considered. Click To Tweet
Attempts to evaluate enzymatic changes and mitochondrial adaptations are still in their infancy, but as the science and technology evolves, so does the validity and accuracy of those measures. Mitochondrial changes can’t be specified but inferred at this moment in time, and local adaptations of muscle groups, specifically large superficial ones, are inferred as well. Generally, the rise and fall of muscle oxygenation (SmO2) locally to the tissue monitored is the primary pursuit of NIRS in sport. Observation of those values, with context in training, enables practitioners to know exactly how the body is responding to both training and rehabilitation.
Brain function is an extremely complex interaction of a highly evolved organ and the cooperating nervous system. Some research on fNIRS demonstrates enough value that monitoring frontal activity with sensors is warranted. Both performance sport science and the supportive nutritional space uses non-invasive real-time monitoring to explore the relationship between nutritional protocols and sports performance outside of general testing. As the field evolves, the connection between decision-making and other cognitive abilities and simpler measures of performance is expected to grow, and fNIRS is one of those technologies that will improve the outcomes of both the researcher and practitioner.
Who Should Use a NIRS Monitor?
Those involved with sports performance, sports medicine, and even sports nutrition are users of NIRS in both practice and research. NIRS can, with the right interpretation, represent important change within the body. The data collected from NIRS technology is very actionable, as testing or monitoring is very effective in improving the precision of the training, down to the cellular level. Based on the power of NIRS monitoring, those who need better outcomes in training should use the technology to evaluate the treatment and training methods used.
Sports medicine professionals monitor local changes to injured areas with an array of technologies and clinical approaches. While electromyography is common, the muscle activity readings are often not enough to make decisions and adjustments. Muscle injuries are often monitored by perceptual pain and soreness feedback, and symptom tracking causes possible physiological problems that objective functional measures do not. Supporting athletes with novel approaches to tracking injuries is useful and very practical.Those needing better training results should use NIRS to assess their treatment & training methods. Click To Tweet
Long-term adaptations to the muscle and acute improvements for deconditioning are difficult to monitor without invasive testing. In addition to the need to have conscious benefits of NIRS testing, the ability to see how rate limiting factors trend is also important, since many of the cardiopulmonary tests may not be explanatory to the athlete’s adaptive response. When athletes improve in conditioning, many of the adaptations can’t be explained by histological and morphological changes to the heart and lungs.
Nutrition science uses both the functional and local forms of NIRS to evaluate research investigations and applied approaches to sport. Sports nutrition is rapidly evolving now, as the counseling model is now transforming to more applied coaching methodologies. The evaluation of dietary and supplement interaction with training is growing, and it’s expected that NIRS will be one of those tools for sports nutritionists.
Strength coaches may wish to use NIRS technology for speed and power training, as rest intervals are often based on estimated time periods rather than true physiological changes. Training with speed and power requires both the knowledge of output changes and the underlying reasons for those changes. Using NIRS with conventional monitoring systems is empowering for coaches who need the explanatory information for why some athletes may not respond to programs and why some athletes do make improvements with similar training protocols.
Muscle Oxygenation Hardware and Software
Most sensors in sports need to be very small in order to be wearable or ecologically valid. Sensors with enclosures that are awkward or too large will change the validity of the reading, because athletes will alter their movements to accommodate the system. Sleeves, socks, bodysuits, and other garments are necessary to block light from the sensor area, otherwise the data will be corrupted. In addition to the light sensors, it is common that the product includes telemetry options such as Bluetooth, ANT+, or local Wi-Fi ability. Battery and wired power options are common now, and most research-grade products tend to use laboratory designs that are not portable or useful for field testing.
Exporting data into comma separated values (.csv) is nearly standard with most of the systems, but the new wave of consumer products will likely have fewer export options as the app software is geared to the direct-to-athlete service. Third-party software and integration is very common, whether added value systems or athlete management systems that are powerful enough to display testing and/or training data. Research-grade products mainly export into .csv or provide their own file format to allow backing up of native data.
TrainingPeaks, Stages, Today’s Plan, and SportTracks all work with the Moxy Monitor for data integration. Several added value software programs such as GoldenCheetah, PerfPRO, PeriPedal, and SelfLoops are popular with cyclists and triathletes. Most of the third-party added value systems are designed to work with Moxy, but a few are in the works to be universal as the market evolves.
The Current Near-Infrared Spectrometry Products in Sport
Muscle oxygenation measurement is a major role of NIRS, but other systems exist that use near infrared spectrometry to calculate physiological changes in athletes. A few of the sensors are ways to replicate lactate curves while others look at brain performance, thus making the market wide and innovative for companies to provide solutions to mounting conditioning and physiological challenges. Here are seven products that are available now (Autumn, 2018) and are either designed for sport or can be used by those involved in sport.
Humon is a Boston-based company with a commercial system that is similar to BSX, as it focuses on the lactate modeling of the body and is designed to fit the general recreational athlete. Humon Hex is new to the market and promoted to the mainstream consumer. In addition to the single location sensor, the product offers an app on both the iOS and Android platforms to connect to the sensor via Bluetooth, and has a web application for more advanced analysis post use. Humon markets a virtual coach for their platform, a claim that suggests their artificial intelligence provides enough insight that changes in training recommendations are possible from their analytics. The system is water-resistant, offers a wireless charger, and can be purchased online.
Moxy Monitor is one of the top-selling solutions in endurance and team sport domestically and its international reach is growing as well. In the summer of 2018, Moxy improved both the hardware and firmware for more convenient measurement, and expanded their educational services with another user conference. Much of Moxy Monitor’s traction is in the endurance sport market, but a growing interest from speed and power sports is projected to be significant, thanks to their hardware improvements. Moxy Monitor can be purchased online directly, or through resellers at local facilities and e-commerce stores.
The PortaMon is a leading system on the market, and has been evaluated multiple times as both reliable and useful for coaches demanding performance in sport. As its name suggests, the system is portable and extremely versatile, allowing coaches to use it in multiple assessments. The PortaMon product is sold by Artinis, a Dutch company that provides an fNIRS system as well. In fact, Artinis has multiple NIRS systems for all types of scientific needs, including sports performance and research. The company sells their products through distributors, and specializes in other medical devices outside the NIRS market.
NIRx provides the NIRSport solution for researchers needing mobile tracking beyond just the brain. The German company also provides solutions for monitoring eye function. The NIRx line of systems is not just for sport, as the company is interested in supporting an array of other areas such as neurofeedback, as well as child and infant monitoring and research. NIRx does have distributors and offices outside of Berlin and, according to their website, their software solutions are constantly being refined and updated.
This research product is mentioned as an example of a cerebral oxygen monitoring solution that is commonly used for investigations outside of sport. The system is not a medical device and is not appropriate for coaches or even sport scientists in applied settings. MetaOX is sold through ISS, the company that provides a major line of research-grade products outside of NIRS. Including the cerebral products, medical lines that support infant care and medical grade monitoring are also available. The company has not entered the sport monitoring space with a wearable, and is unlikely to provide anything in the near future outside of what they provide to kinesiology and sports medicine applications with altitude and hyperbaric areas.
This company is another Massachusetts-based provider of NIRS, and they specialize in brain mapping and not sports monitoring for conditioning. Their system is for clinical and research needs only, and their other products help with breast imaging, cognitive development, and other research. The strength of their innovation is perhaps the brain mapping software, as they do provide a real-time concentration solution. TechEn, the parent company that manufactures and develops the NIRSOptix, has prestigious partnerships with the Harvard Medical School and Massachusetts General Hospital.
A small but visible company, Nirox provides a miniature NIRS device that is sport ready. The Italian company also provides consulting services along with their research and wellness product line. Based on hardware specifications, the equipment is wireless for the NIMO wellness product and the tabletop version is appropriate for research as it’s not very mobile. Most of the company’s products are industrial and medical sensors outside of sport, and the traction with teams and facilities is virtually non-existent.
Other systems are likely to follow these leaders with similar features, pricing, educational resources, and access to experts in the field. It’s wise to look into the company’s history and goals before making a purchase, as new startups and brands have come and gone, like all sports technology. BSX Insight closed its doors recently, and companies that depend heavily on fitness enthusiasts will likely be more volatile in sales and revenue.
Additional Recommendations on Body Oxygenation Systems
The current options in sports performance and sports medicine are already available now. Before implementing monitoring of muscle oxygenation, or any variable for that matter, you need education on the subject matter and training on how to use the system of choice. In addition to education, it’s also important to know the limitations of the technology used and when other methods are appropriate for monitoring. Down the road, the science of muscle oxygenation and similar physiological monitoring will be more accessible for coaches to apply, as we expect even more commercial opportunities to come to market.